The influence of the refractory investment on the development of porosity in cast structures.

Four series of standard tensile specimens were produced by casting into moulds composed of silica bonded, gypsum bonded, and phosphate bonded refractories. Two nickel base alloys were employed, one a standard dental casting alloy and the other a specially formulated ductile material. Subsequently, all specimens were subjected to mechanical testing, and radiographic and metallographic evaluation, in conjunction with porosity determinations, in order to ascertain how the nature of the refractory investment influences the structural quality of the castings produced.